99 Ranger, 3.0 V8, PSPB, air, cruise. This has not happened often enough to describe too explicitly but sometimes shortly after I shut the engine off I'll hear a whistling noise -- it's short in duration and 1 or 2 whistles and it sounds exactly like someone whistling a low note. It appears to be coming from under the hood on the right side. The location is hard to pin-point because if I try to listen for it, it probably won't happen. Anyone experience this ?

anyway... on a more serious note, it may well be a vacuum leak somewhere in the system. if so, that's a bad thing... and worse if it's a low note, versus a high note, because that would imply that the void is large, rather than small.... have your vacuum system checked out by a mechanic.

I checked, and sure enough, someone has stolen 2 cylinders from my V8 and now it's a V6 ! I'll need to replace them -- maybe I'll add 2 more and make it a V10. A vacuum leak would be my first suspect as well. Previous to my post I did a cursory look and will look further. Since I hear it after I shut off the engine it must be from a "stored vaccum". The leak probably occures every time but has to be just right to produce the whistle. Everything seems to operate normally.

It's winter here but it may be running during defrost. I'll keep that question in mind and try to determine if it happens after the compressor has been running. What in particular would that point to if that is the case?
Thanks for the reply(s).

Jim -- keep in mind that the A/C compressor runs, even when you're using the heater in the Rangers.

I think the possible point Paul may have been alluding to is that you may be hearing a 'normal' noise from the A/C compressor... or, I dunno, perhaps an abnormal one. I occasionally hear mine 'de-compress' (if you will..) after I park the truck -- not really a "whistling" sound like you described, though.

I'm willing to bet there's an old confederate soldier sittin in the vicinity of your truck whistlin the first two notes of Dixie, but shutting the engine off scares him away, until the next time he decides to try again.

That's just my theory though, and probably not likely.

In all seriousness, i'd agree with turbo, most likely the A/C compressor "de-compressing", yours just sounds different for some reason.